1. Field of the Invention
The present invention relates to an image heating apparatus to be preferably used as a heating-fixing device of a copying machine or a printer using a recording system such as an electrophotographic system, electrostatic recording system, or magnetic recording system.
2. Related Background Art
In the case of an image heating apparatus such as a heat-fixing device mounted on a copying machine or printer, a separation claw contact-set to the surface of a fixing roller to forcibly separate a fixed recording material from the fixing roller is known as means for preventing a heated and fixed recording material from winding around the fixing roller. However, because the separation claw easily scratches the surface of the fixing roller because of its mechanism, there is a problem that scratches on the fixing roller due to the separation claw are transferred to an image when fixed to deteriorate the image quality. Moreover, in the case of a fixing apparatus using a flexible sleeve instead of the fixing roller, it is difficult to a separation claw for this use.
Therefore, a configuration is used in which a fixed recording material is curvature-separated from a fixing roller or fixing film by using the curvature of the fixing roller or fixing film.
However, the above fixing apparatus using no separation claw has the following problems.
A recording material is supported by one point of a fixing nip portion from the time when the leading edge of the recording material in its carrying direction passes through a fixing nip portion up to the time when it reaches a discharge roller. Therefore, under the above state, the carrying behavior of the above leading-edge region is unstable. Particularly, in the case of a recording material made of a thin paper having a weak kneed or an OHT and the like film which is extremely weak-kneed when heat is applied, the recording material easily winds around a fixing roller because of being influenced by the adhesion between toner and a fixing roller. Moreover, when the carrying (conveying) direction at the fixing nip portion of a fixing apparatus is almost vertical, the escape angle of the recording material from the fixing nip portion becomes vertical. Or, the image face of the recording material turns downward and thereby, the recording material easily winds around the fixing roller because the gravity is added.
When the edge of the recording material in its carrying direction is discharged toward the fixing roller contacting with a toner image on the recording material while slightly winding around the roller, excessive heat is added to the leading edge of the recording material in its carrying direction. Therefore, a problem occurs that the toner image is hot-offset the image quality is easily deteriorated. Moreover, a problem occurs that the recording material twins around the fixing roller and is easily jammed.